Hi, i'm an AE user switching to NUKE. i'm trying to recomp my composites from ae to nuke but i'm stuck with masking out edges of my smoke footage. The smoke footage i'm using has no alpha. I want to foreground layer the smoke in multiply mode (so the whites will be transparent) then mask out the edges of it. i tried to connect the smoke footage to a COPY NODE then connect my RotoPaint node then Premult it then connect to a Merge node. Inside the merge node, over mode, my mask is ok but i need to set it to multiply. but when i set this to multiply the masked out layer turns black. i also tried to switch the "alpha masking" on, again the masking is ok but the white are there again.

Here's a screenshot;

http://www.elementalfx.net/masking.jpg

fandalis

08-19-2010, 12:17 AM

BTW, i'm using nuke 6.1 PLE. thanks a lot in advance!

scrawford

08-19-2010, 01:00 AM

You could just merge the smoke over the dog, and plug the mask into the mask input of that merge.

scrawford

08-19-2010, 01:02 AM

If you had to take care of it before the merge, you would need to merge white over your smoke where you didnt want it to show since you are multiplying in the merge. Right now when you premult your alpha you are creating pixels with rgb values of 0. When 0 is multiplied by the color of the dog your just getting 0 back.

fandalis

08-19-2010, 01:25 AM

you mean like this? the smoke is again not multiplied...

http://www.elementalfx.net/masking2.jpg

fandalis

08-19-2010, 01:32 AM

If you had to take care of it before the merge, you would need to merge white over your smoke where you didnt want it to show since you are multiplying in the merge. Right now when you premult your alpha you are creating pixels with rgb values of 0. When 0 is multiplied by the color of the dog your just getting 0 back.

yes that's what i've been thinking... is there another workaround for this?

MasonDoran

08-19-2010, 10:40 AM

Technically, smoke should be used as "over" because it does not darken or multiply and is actually opaque particles preventing you from seeing the image underneath. The alpha is needed to control how much you see. Artistically of course, you may want a different effect.

Why not use a luminance key to create your alpha of the smoke, add a roto to clip the falloff, and just use over blend mode?

To get some kind of darkening effect, you can then use the alpha of the smoke and grade the image beneath the smoke.

Hey thanks! I'm trying to work this out right now. Is'nt there a bezier node tool in 6.1ver? or was replaced by the rotopaint node in the latest version. coz i tried your script and the masking is working fine but when i replace it with the roto or rotopaint node the blacks are there again. i compared/inspected your parameters to mine i think they are set fine. i will do a screencapture after this.

fandalis

08-20-2010, 10:12 PM

here is the screen capture
http://www.elementalfx.net/masking3.jpg

MasonDoran

08-22-2010, 01:23 PM

Roto replaces bezier and works a bit differently although is essentially the same, you will have to manually control the alpha output in the Roto node.

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